Hemiparesis from stroke is the leading cause of disability in the world. Arm impairment after stroke is due not only to weakness, but also to impaired muscle coordination?abnormal co-activation?during attempted movement. This is especially true in the most severely-impaired patients, who are most in need of new treatments. We have developed a myoelectric computer interface (MCI) paradigm to remedy this co-activation. The long term goal of this research is to develop an affordable, wearable MCI device that will improve motor function in stroke survivors. However, to date we have studied MCI use only in chronic stroke survivors in the laboratory, using cumbersome and expensive equipment. Little information exists as to how soon after stroke abnormal co-activation starts to impede arm function, but it seems likely that averting it would be easier in the acute stage, when the brain exhibits greater plasticity. Moreover, as healthcare resources become ever scarcer, it is important to design new therapies that are portable and affordable to enable extensive use in the community. The objective of this proposal is to advance the MCI paradigm by 1) creating a wearable MCI device that can be used outside the laboratory, 2) enhancing the training regimen, and 3) testing the MCI in stroke survivors in both the acute and chronic stages of recovery. The central hypothesis of this proposal is that making MCI therapy more intense, more similar to everyday movements, and starting training early in stroke recovery, will result in even greater functional improvement. We will design a wearable device and test this hypothesis in stroke survivors in both early and late stages after stroke via these specific aims: 1) To design and implement a wearable MCI device that controls therapeutic, tablet-based games, 2) To develop and enhance home-based MCI training in chronic stroke survivors, and 3) To assess the effect of acute-phase MCI training on stroke survivors' movement and function. This proposal's innovative development of a wearable device paradigm to reduce abnormal co-activation will enable us to study the benefits of MCI training both early and late after stroke. Achieving our objectives will be significant because it will address unmet needs to develop new treatments for stroke that are inexpensive and wearable to enable widespread use. We expect MCI training will help people with severe arm impairment as well as those with moderate impairment, since the severely-impaired have more abnormal co-activation and since the MCI only requires some residual myoelectric activity, not overt movements. We also expect this proposal to provide an unprecedented characterization of the temporal development of abnormal co-activation early after stroke. This will impact our overall understanding of the process of recovery from stroke. We expect that the MCI paradigm will be synergistic with other therapies, since it has a novel mechanism of action (reducing co-activation using EMGs). Finally, we anticipate that this proposal will provide critical results that will position us to translate this research into clinical trials.